An optical sensor is provided with a photodiode (D1) which receives light in a first range, including light to be detected, and a photodiode (D2) which receives light in a second range other than the light to be detected. For instance, the photodiode (D1) receives light at all the incident angles, and the photodiode (D2) has a light blocking film on an incident light path so as to selectively receive only the incident light from the oblique directions. The differential between the output from the photodiode (D1) and that from the photodiode (D2) is read out as sensor output.